1. Field of the Invention
The present invention relates to an iris circuit of a video camera, and more particularly to an iris circuit which can automatically adjust the iris of a camera lens according to the magnitude of a NAM (non additive magnitude) signal which is provided by taking out the highest value from the peak values of red, green and blue color video signals.
2. Description of the Prior Art
In the conventional iris circuit, a parabola signal and a vertical sawtooth wave signal are compared with each other and amplified by a comparison amplifier. A gating pulse is generated by inverting the output of the comparison amplifier with a switching transistor, and gates a predetermined range of the NAM signal provided through a buffer. The gated NAM signal is integrated and amplified by an integrator and an amplifier respectively and then inverted and amplified by another amplifier to which a control voltage is provided. The iris of the lens is made to open or shut depending upon the inverted and amplified control voltage. However, such an iris gating circuit must be complicated in order that the iris may not be affected by the sky or by strong rays of light. Accordingly, it not only causes the manufacturing cost to go up but also involves a problem in that a picture is taken doubly because the iris is not shut even when a built-in shutter is used by turning on a diascope switch.